While the proposed gas storage vessels may be applied in automatically maintaining a particular pressure in items such as cans and other types of containers for dispensing or spraying fluids, and even for blowing automobile tires, an immediate need appears to exist in the field of carbonated beverages; therefore, the description is presented in terms of examples relating to beverages.
Carbonated beverages contain CO.sub.2 gas dissolved in the liquid of the beverage. It is the CO.sub.2 gas that makes a cold drink particularly refreshing. These carbonated beverages are, for the most part, packaged in thin plastic containers made out of ethylene terephthelate and shaped in the form of bottles, with a standard metal cap covering the opening at the top, (the "conventional" bottle). Each time the beverage container is opened, the CO.sub.2 gas at the top of the container escapes, reducing the pressure at the surface of the liquid to atmospheric. The pressure remains atmospheric as long as the bottle remains uncovered, while continuing to lose CO.sub.2 bubbles from the body of the beverage. After replacement of the cap, CO.sub.2 gas from the remaining beverage continues to escape into the space over it, but at a rate which is slowing down as a pressure equilibrium inside the container is approached, at a pressure lower than before opening the bottle. Further, with each opening and with beverage being consumed, a greater volume is left in the container to be filled with the CO.sub.2 gas escaping from the smaller amount of remaining fluid.
Depending on the time lapse between openings, the time the bottle remains open, and the amount of beverage dispensed each time, the beverage may be depleted of its CO.sub.2 gas to a lesser or greater extent and lose its refreshing quality, the beverage becoming "flat".
Part of the problem has been given a solution, but only for the case of the seltzer water in terms of two commercially available dispensers: (1) the traditional "seltzer bottle" and (2) the "Soda Spritzer Bottle".
In both types of bottles the seltzer water is made by mixing water and CO.sub.2 at a relatively high pressure of about 7 atm. (kg/cm.sup.2). As these bottles, while they are being filled, must withstand much higher gas pressures than commercial plastic beverage containers, they need to be stronger, and heavier and are, therefore, more expensive. The traditional seltzer bottle consists of a thick glass bottle capped with a cap that provides a spout, a lever-operated valve for dispensing the beverage and a syphon tube reaching near the bottom of the bottle. During manufacture the seltzer water is produced by simultaneously feeding water and CO.sub.2 gas under a pressure of about 7 atm (kg/cm.sup.2) into the seltzer bottle. The empty seltzer bottle is returned to the manufacturer for refill.
The soda spritzer bottle comprises a container made of aluminum with a wall thickness of about 1/8 inch, (0.3175 cm) and also provides a spout, a valve handle and a syphon, as in the case of the traditional seltzer bottle, for dispensing the beverage. In addition it provides a port for a disposable CO.sub.2 cartridge. The consumer manufactures his own seltzer water by filling the container with water, then introducing CO.sub.2 by puncturing of the cartridge. Additional cartridges must be purchased to make more seltzer. The improvement in these types of bottles over the conventional bottle is two-fold: (a) proportionately more CO.sub.2 gas is packed into the seltzer water because of the higher pressure than can be withstood by the container, and (b) the cap remains "on" until the entire amount of beverage is consumed. Therefore, there is no loss of CO.sub.2 gas due to the opening of the bottle, and the pressure in the empty region at the top of the bottle remains above atmospheric until the entire amount of beverage is dispensed. In both types of bottles the beverage is being dispensed when a hand-operated lever, positioned at the top of the bottle, opens communication between a spout extending from the bottle, and a syphon tube which extends to the bottom of the bottle. The pressure at the surface of the liquid in the bottle then forces the beverage to flow from the bottom of the bottle, through the syphon tube and the spout to the glass, while the gas, which is trapped at the top of the bottle, is preserved.
While the loss of the CO.sub.2 gas through the process of opening the beverage bottle has been eliminated by the use of the above special containers, the amount of CO.sub.2 per unit volume of liquid in the container is still being reduced every time beverage is withdrawn from the bottle. The reason is that for any volume of liquid lost from the bottle, there is an equal volume increase in the empty space at the top of the bottle. As this volume increases, its pressure is reduced and more CO.sub.2 gas evaporates into it from the beverage, to keep the pressure at both sides of the liquid surface equal. The net effect is for the beverage to continuously lose CO.sub.2 gas and become more and more "flat" as the amount of the beverage in the bottle reaches the end; although not as flat as in the case of the conventional bottles.
The thin plastic bottles made out of polyethylene terephthalate, used for most of the carbonated beverages are incapable of handling the high pressures of the seltzer of spritzer bottles. Since these beverages are packed with less CO.sub.2 than found in either the seltzer or the spritzer bottles, and since they lose additional CO.sub.2 with each opening of the bottle, a quick deterioration through depletion of the beverage's CO.sub.2 gas occurs in the conventional commercial beverages.
In the case of non-carbonated wines it has been found that the natural taste of the wine can be better preserved when the empty space in the wine bottle is filled with Nitrogen gas rather than air.
In another patent application titled Pressurizing Dispensers for Preserving Carbonation in Beverages, Ser. No. 07/258893, filed Oct. 17, 1988, claims have been allowed covering an apparatus for dispensing a carbonated beverage from its own bottle while the bottle is covered by a special cap. The special cap with which the bottle's own cap is replaced upon opening the bottle, provides (1) an output port to which the dispensing apparatus can attached to a dispensing spout and on which it can apply a force for opening an internal valve to allow the beverage to flow to the spout and (2) an input port through which the dispensing apparatus feeds CO.sub.2 gas at a predetermined pressure to fill in the volume generated inside the bottle as the beverage is being dispensed.
While the above dispensing apparatus can be functional in maintaining a desirable pressure inside a beverage bottle for preserving the taste and propel the beverage, it presents drawbacks in terms of the expense for the average consumer of acquiring such an apparatus and the nuisance of keeping an additional item on the top of the counter or the dining room table. In addition, the mechanics of having to operate an internal valve from outside the bottle also translate into cost.
A primary aim of the present invention is at providing simple means for correcting the problem of the CO.sub.2 loss in carbonated beverages and especially in those sold already made in thin conventional plastic bottles, by maintaining proper pressure during and after dispensing of the beverage.